Disclosed are processes for the preparation of elastomeric conductive materials involving combining at least one conductive polymer with rubber latex, at least one organic acid, at least one oxidant, a pH stabilizer, optionally an organic solvent, and optionally at least one surfactant. These materials exhibit excellent strength, elasticity, and conductivity. Upon drying are already doped throughout the surface and bulk of the material, eliminating the need for a surface doping (chemical oxidizing to create conductivity) process step.
The U.S. market for conductive polymers is about 230,000 metric tons annually at an estimated 2008 value of $1.52 billion. The global market for electroactive polymers was $1.9 billion in 2010. This market is forecasted to grow up to $3.05 billion by 2016 at a compound annual growth rate of 6.1%.
The materials are used in polymer batteries, static discharge devices, pressure sensors, organic light-emitting diodes (OLEDs), electronic ink, antistatic packaging, material handling, work surfaces & flooring, printed circuit boards, etc. A growing market segment is the medical industry where conductive polymers are used as components for electrical implants, nanowires within microfluidic circuits, in medical robotics, prosthetics, and as electrodes/sheathes for electrical detection or stimulation.
Polymeric conductive composites can be made from many polymers using conductive materials as fillers. Usually the fillers are carbon black, carbon fibers, metallic powders, and fibers coated with metals. The carbon black filled composites, although low in cost, have high percolation thresholds for electrical conduction and the conductivity cannot be controlled. Composites with metal powder fillers have high percolation and density, and the electrical conductivity can likewise not be controlled and the metal can become oxidized thus reducing the effective electrical conductivity of the composite. Use of other conductive fillers such as nickel coated carbon fiber and carbon nanotubes are limited due to cost.
Inherently conductive polymers (ICPs), such as polyaniline, polypyrrole, and polythiophene, are used alone or in composites with conventional polymers to create all-polymeric, clean, and permanently conductive materials, overcoming many of the disadvantages of filled materials; see, for example, Stat-Rite® by Lubrizol and PermaStat® by RTP. Polyaniline (PANI) is a conducting polymer which has been extensively studied due to its environmental stability, simple methods of synthesis, high conductivity (102 S/cm), and relative low cost. Moreover it can be readily doped/dedoped to modify the conductivity. Polyaniline's structure is as follows:
However, due to its poor processability and mechanical properties, commercial applications of neat PANI are limited. Incorporation of polyaniline into a host polymer substrate to form a blend, composite or interpenetrated bulk network has been investigated and different techniques have been used for such intentions. Synthetic elastomers and thermoplastics elastomers have been investigated as matrices for hosting conductive polymer. The techniques utilised to obtain these elastomers blends include thermomechanical mixing, solution mixing, electrochemical methods, and in situ polymerization. The elastomer blends obtained with thermomechanical mixing showed poor conductivity for some applications, and solution mixing and electrochemical methods are limited by these processes to thin films of material.
We have developed processes for producing an elastomeric conductive material as a composite of, for example, polyaniline (and its derivatives such as poly(ortho-ester aniline) (POEA) and poly(ortho-methoxyaniline) (POMA)), with natural rubber thorough polymerization in situ of aniline in natural rubber latex. The use of natural rubber (NR) offers a non-petrochemically-based major component in a low VOC (volatile organic compound) process.